This invention is in the field of transistorized amplifier circuits, and relates more specifically to linear transconductance amplifier circuits.
The basic concept of using a differential correction amplifier to provide a correction signal to a main amplifier is shown in U.S. Pat. No. 4,146,844. In the circuit disclosed in FIG. 4 of that patent, there is shown an amplifier circuit having a correction amplifier which takes its input from the collectors of the two inputs transistors of the main amplifier. This circuit, however, is relatively complex. Furthermore, since the correction amplifier does not see the same signal as the main amplifier, cancellation of nonlinearities is not optimum, and transconductance will be dependent upon base-emitter voltage (V.sub.be) and transistor current gain (.alpha.). The correction amplifier used in FIG. 4 of U.S. Pat. No. 4,146,844 is of the type having two transistors (100, 102) with their emitters connected together by a single resistor (105), and a current source (110, 108) from each emitter to a source of reference voltage.
In U.S. Pat. No. 4,048,577, FIG. 5a shows one form of a gain cell circuit used to provide improved bandwidth. This circuit utilizes a compensation amplifier of the type in which the emitters of the two transistors forming the differential compensation amplifier are connected together by two resistors (21, 23) in series, with a current source being connected from their common junction to a source of reference potential.
While the circuits of the invention bear certain superficial similarities to portions of the configurations described above, none of the known prior art configurations combine these circuits in the manner disclosed herein or provide the necessary relative gain ratios to obtain a simple configuration in which low distortion is combined with linear operation over a wide dynamic range.